Detection of breaks in flexible elongate members

ABSTRACT

In a method of detecting breaks in an insulated electric conductor or other flexible elongate member whose surface is of an insulating material capable of generating an electrostatic charge by friction with another surface, the member travels in the direction of its length past and in continuous contact with at least one electrode which is connected to earth or some other charge sink. The electrode (or each electrode) is conductive and of a material chosen to cause electrons to be transferred continuously in one direction between the electrode (or each electrode) and the surface of the member and electrons are caused to flow between the charge sink and the electrode (or each electrode) or vice versa; the current flowing between the electrode or electrodes and earth is continuously monitored, preferably using an amplifier connected across a resistor between the electrode or electrodes and the charge sink.

Unite States Patent [191 Poole et al.

[ DETECTION OF BREAKS IN FLEXIBLE ELONGATE MEMBERS [76] Inventors: John Huyton Poole, l4 Daresbury Rd.; Brian Anthony Goodison, 5 Hard Ln., both of St. Helens, England 22 Filed: June27, 1973 21 Appl.No.:374,023

[30] Foreign Application Priority Data June 28, 1972 Great Britain..., 30284/72 [52] US. Cl 324/32, 324/54, 73/160 [51] InLCl. GOlr 29/12, GOlr 31/12 [58] Field of Search 324/32, 72, 51, 54; 317/2; 73/160 [56] References Cited UNITED STATES PATENTS 2,295,795 9/1942 Keeler 324/32 X 3,324,719 6/1967 Segrave 1 73/160 3,671,806 6/1972 Whitmore et a1... 317/2 R 3,694,736 9/1972 Wakefield.... 324/51 3,753,102 8/1973 Beck 324/32 X FOREIGN PATENTS OR APPLICATIONS 610,855 3/1935 Germany 324/32 5] Jan.7,1975

Primary Examiner-Alfred E. Smith Assistant Examiner-Rolf Hille Attorney, Agent, or Firm-Buell, Blenko & Ziesenheim [57] ABSTRACT In a method of detecting breaks in an insulated electric conductor or other flexible elongate member whose surface is of an insulating material capable of generating an electrostatic charge by friction with another surface, the member travels in the direction of its length past and in continuous contact with at least one electrode which is connected to earth or some other charge sink. The electrode (or each electrode) is conductive and of a material chosen to cause electrons to be transferred continuously in one direction between the electrode (or each electrode) and the surface of the member and electrons are caused to flow between the charge sink and the electrode (or each electrode) or vice versa; the current flowing between the electrode or electrodes and earth is continuously monitored, preferably using an amplifier connected across a resistor between the electrode or electrodes and the charge sink.

7 Claims, 7 Drawing Figures PATENTEDJAN 1m 7 8,859,593 SHEET 10F 5 PATEHTED JAN 5 SHEET 30F 5 I'Thjisfinvention relates of an insulating materialgcapable of genera't ng' an 'elecy causing-the member;tottravelfin the 'direc I I II length past and in continuous contact with at leastlone i sion asused herein includes any 'c harge'sinky -The'elec trode, or each electrode if there is more'than"onjefjis' conductive and of a'material chosen to cause electrjo i g to be'transferredcontinuously'from -the'electrodexo each electrode) tolth'e'surfacejof the member'or, vi

RIIEAKSJQIN FLEX an: I

fin rs: a

GA EMEMBER-S DETEC;

' The invention is'especially, but not exclu tapesor webs or streamsof particles- I -j composite flexible elongate me'rnltjers, .for' exampl e;-j

cable? one of the problemsthatj cable manufacturers are continuously seeking to, overcome'isthatoflthede 31. I 'tection of breaks in'one insulated'c'onductor qr a' pair of co nductofrsduring r'rianufactur'ebf the cable b efo re "twinning or before fa multiplicity of pairs are'asse'mbled together and sheathed. I f brea kagel-in such; flexible elongate "member is-not detected especialliy until after 1 the pairshave b eenassembled'together and a continu iIt-ytes'teffected, either the'cable must berepair'edw considerable difficulty and not inco'nsiderable expense o r-the'c'able must be accepted witli' aI r educed complementof effective pairs or..quads;.";- i

The present invention has for'its princ ipjal iobjec th trostat'ic charge'zby friction with anotherfsurface According to. the-invention the method com electrode which is con nect edjto e'arth (wliieh expres versaahd electrons are caused toTfl'oyv from earth tol'the- I electrode or each electrode) or vice :versa. ln-choosing I the electrode materi'al 'the' material of the-surface of the member is aireleva'nt' factor l' Cur'rentiflowing be-""5 tween the electrode ofele ctrode's' and 'ear th iscontinuously monitored, an interruption" said currentiflow indicating the occurenceof a break:

statically charged b y contact with appropriate -s 1 1 rIfa'ces it may be charged byifrictional-contact-With,rhea-glad. trode or electrodes. w

Preferably the electrode (or each electrode) is con- I the. .etectio'nof breaks inf.

' he continuity of a mater alas thefmate'rial travels past a detectingregion. The materialmay be in the form of II an elongate article that travelsp'ast the detecting'regioni finithe general direction of i'ts lengthorit' may be in the forth stream of intercontactingparticle sof th'eltna. v

' f teri'al 'fo,r instance powdered or granular materiaL S uch elongate articlesand streams of particles will hereinaf" 'ter, forconvenience be included in the generic expre s- I "the-membeLT-hefsurface of the 'e'longate'fimembermay e'i't'her'be electrocontinuously monitored by observing the voltage across the detector resistor. By applying a dc voltage to the electrode or elec- '5 trodes the flow of electrons due to continuous contact between the travelling member and the electrode or electrodes can be increased, the direction of flow depending on the polarity of the voltage.

Where the member or each of the members is an in- 10 su'lated conductor we have found that even with a voltyage of say- 50 V do the flowof electrons to the surface 3 of the insulated conductor of each of them can be uppreciably increased. However, with a view'to'avoiding I 'vely concerne'd withthe detection of a; break in a flexible el o'n-" v gate member which for instance might be one'insulated t conductor, or a pair of insulatedelectricconductors;I .The invention isl also?applicable to the detection ,of Z' breaks 'in'single threads or,- str in gsi" or other sing-le o r f spurious effects otherwise caused to the current flow by fllS bare portio'ns of the insulated conductors, and espeelectrode or electrodes.

20f T 'e invafion also includes apparatus for use in the I I I I I v method of'the inventiom'whichapparatus comprises at lnthe manufacture of'an electric cableconiprising a ii multiplicity of singleicon'ductor s or: pairs off insulated Jconductorsof 's'inalldiameten; for example a telephone least oneelectrode havin g' a-surface of amaterial capa- I ble'ofgenerating:anelectrostaticcharge on-the thember. or,'dischargi ngan electrostatic 'cha'rge from the 25 membe anq off such a forjmith'a't, 'a flexible elongate mfember 'canflbe icaused to travel in-the' direction of .its

length past' aridfinqpontinuoIus contact'withthe elec- I I yfmonitorihgcurrent flow be- -tween the said electrode o'rfe l'e'ctrodes andfe-arth.

earth; P'THe-in ventidnlwm be further I Q continuously I niDni't 'r-ing insulated: conductors for a b'reaks ;=witli reference to the-accompanying drawings; t 1 -i0f its in he m Inufactu're -of 'rnul ticond'uist orcable";

' sh'owniin electrodes 1 are connected-miseries to earth throu gh'Fa f-"resis tor .3 a resistor- 4hr lOfMl'Conn'ected I across the resistor 4 (is a shieldedtamplifier G to tt heout- I prefer to apply a voltage of'about -"2 O0 V dc to the Preferablythl'apparatus' also inc'lude'san amplifier connected across th'elresistor, them onitor ingmeans. being cionriectedto} and adapted to me asu're'fthe volt; Uage' utput 'of ytheamplifierflf.desired'za source of dc 4' v ltage-ma be connected betweenthe; resistor and tion, way l ofl example offpreferred i lappa'ratus' for I II I showgdiagrammatic epresentations-sof:J,

fthree forms,of apparatustijnfaccordanc'ewithfltheinvert 7 showapractical-form of app'aratus for use I I FlGylj comprises three e |o n gatI steelJe gtirodes (1 each ititheformbf a'stee l rod I I, mounted'onand projecting fromila's'upport'2 of'in Sula t-L II 1 m'gmatjerial.withjheir -ax essubstantially parallelo rieg withanothe Theiaxesiof tweorjthe electrodes} l i e in I ma -n hor onta l- 'pl' ane 'andthe thi rd eleetrode.is I j two' eleictrodes and; above thee". j commonplaneofthe a'x'es 'a'ndis adjustable andIorj r eQ 'alreadym unted f srm vement in a substantially verti cal-directiontit-accommodateconduetors-or conductor I pairs"'offd'ifferentoverall diameters passing in cotitinw- H I w I I douscontaet' between-Ethe electrodesas indicated; 'l'hel,v as is frequently the casein te'xtile'and cable m'akingitn chinery before'it reachesthe electrode or electrodes or" passed the electrode and FIGS. 1 and 2 show diagrammatically a positively charged member for this purpose.

FIGS. 4 and 5 illustrate a practical form of electrode assembly for use in monitoring the movement of a large number of pairs of insulated wires 11 advancing parallel to one another towards the point where they are to be stranded together. The stainless steel electrode rods 1 are 9.5mm in diameter and long enough to accommodate any anticipated lateral movement of the wire pairs. For each wire pair there are two fixed electrode rods 12, mounted in an acrylic (Perspex) panel 13 which is 25mm thick, engaging the underside of the wire pair and a single central adjustable electrode rod 14 mounted in a slideable acrylic rod 15 and passing through a clearance hole in the panel 13 so that the pressure between the electrode rods l2, l3 and the wire pair 11 can be adjusted by a screw 17 to accommodate conductor pairs with different dimensions and- /or different flexibilities.

FIGS. 6 and 7 show a suitable electrical circuit designed so that it can be arranged, if desired, to give an output alarm signal only if the number of broken pairs exceeds a predetermined acceptable level.

Each group of electrode rods 1 is connected by a screened cable to an individual primary amplifier unit 18 (FIG. 6) only one of which is shown in detail. The input current is taken through resistors R1 (100M) and R2 (10M) to the local voltage reference on line 23 which is 200\ with respect to earth and to which all screens are connected.

Transient currents are shunted by a by-pass capacitor C1 (2.2n). The signal current flowing through R1 is typically of the order of l nA and to ensure effective response, the amplifier Al must have an input impedance large compared with R2 and an input bias current small compared with the signal current. An operational amplifier with an F.E.T. (Field Effect Transistor) input is available from Burr-Brown Research Corpn, of International Airport Industrial Park, Tucson, Arizona, or from Burr-Brown International of 25A King Street, Watford, Hertfordshire, England, and has been found satisfactory. This has an input impedance of 10 ohm and 3 pF and an input bias current not exceeding 25pA at 25C (doubling for each 10C temperature rise).

The amplifier input is protected against overvoltage by diodes Dl-D2 (type PAD l) and the gain of the amplifier determined by a voltage divider R3 (1M), R4 (1K), resistor R (10M) being selected to minimise the input offset due to bias current and noise. Variable resistor RVl 10K) is adjustable to set the input offset to zero, and capacitor C (SpF) inhibits oscillation at the cross-over point of the amplifier. R5 (45K) is the load resistor of the amplifier and diode D3 (type IN 914) ensures that only positive outputs can be fed to the line 19. Here and elsewhere in the circuit diagrams power supply input is indicated simply by terminals 20.

Owing to the stochastic nature of the electrostatic charge-transfer process, the output at line 19 varies unpredictibly within a range of positive values, and to allow meaningful summation of the signals relating to the separate wire pairs, it is next converted to a sub stantially constant value by a logic gate L. A solid-state device is preferred, although it would be possible in principle to use a relay. In particular, the solid-state logic device sold by RCA International Ltd of 50 Curzon Street, London W1 as the Cosmos Exclusive-OR gate is preferred. The output voltage signal from the logic gate L when the voltage on line 19 is substantially different from the local voltage reference (line 21) is constant (to an accuracy better than the reciprocal of the number of wire pairs being monitored) and does I not vary with the magnitude of the input voltage in its working range. Ifthe input signal disappears the output falls to zero (to the same degree of accuracy).

The logic output signals in respect of all the wire pairs are summed by a resistance network comprising individual resistors R6 (22K) and a common resistor R7 (270) to obtain at 22 an output signal voltage which varies linearly with the number of input signals: on failure of any individual input signal, the corresponding R6 is effectively placed in parallel with R7, drawing additional current from the other logic devices and so producing an enlarged voltage drop across the other R6s and reducing the voltage across R7.

Referring now to FIG. 7, the output signal from the part of the apparatus shown in FIG. 6 is amplified by amplifier A2 and fed to upper and lower limit comparators C01 and C02, respectively. Reference signals dependent on the number of wire pairs being stranded are derived from a switched potential divider network comprising a double-pole decade switch S1 controlling two series of ten lOO-ohm resistors R8 and setting tens of conductor pairs and a single pole decade switch S2 controlling a single series of ten lK resistors R9 and setting units of conductor pairs. Resistors R10 are selected to ensure an appropriate input voltage range for the amplifier A3 which supplies an upper-limit signal to the comparator C01 and also a related lower-limit signal via a network comprising amplifier A4 to comparator C02. The relation between the upper and lower reference signals, which determines the number of broken pairs that will be tolerated, may be made adjustable if desired by using variable components in the network of amplifier A4. Amplifiers A2-A4 may all be of the kind sold by National Semiconductors Corp of 2900 Semiconductor Drive, Sante Clara, California, or from National Semiconductor (UK) Ltd of the Precinct, Broxbourne, Hertfordshire, England as type LM 301A and the comparators C01 and C02 may be of the type sold by Burr-Brown Research Corpn and by Burr-Brown lnternational (whose addresses are given above) as type 4082/03.

Appearance of an output signal from C01 indicates that the number of wire pairs detected exceeds the number set on the decade switches (normally due to a setting error), whereas an output signal from 2 indicates that the number of pairs detected is lower than the set number by more than the built-in (or pre-set) tolerance.

In normal operation, any output signal from either of the comparators is fed to a relay Re 1 which closes contacts Re 1/1 to illuminate an alarm lamp Ll energised from a tertiary winding of the mains transformer T. The relay Re I also closes latching contacts Re l/2 to maintain itself energised from the power supply for comparator Col until re-set by the normally-closed manual switch S3. The relay Re 1 may have additional contacts Re 1/3 for operation of a machine-stop control.

To avoid difficulties in starting, the relay Re 1 is only connected by a second relay Re 2 in turn controlled by a centrifugal switch S4 when the cable stranding machine reaches a predetermined speed. An indicator lamp L2 may be associated with this switching action, and a mains indicator lamp L3 may also be provided.

As already indicated in describing FIG. 6, the line 23 is maintained at 200 V with respect to earth; this voltage is established by the secondary of Transformer T in conjunction with Diodes D4 and a conventional resistame/capacitance smoothing network.

The apparatus shown in FIGS. 3-7 can be used to detect breaks in a pair of insulated conductors (telephone pair) each having a conductor diameter as low as 0.3mm and conventional thickness of insulation and can be operated at speeds down to approximately 5 metres/minute.

The invention has the important advantages that it is simple, provides a quick response on the detection of a break and is dependent on linear movement of the flexible elongate member and neither on rotational movement of a guide or carrier therefor, nor on the loss of tension at the detection point. The apparatus of the invention can be accommodated in the fixed input system in a pairing, quadding, stranding, cabling or other cable-making machine without any necessity to effect any substantial modification to the machine.

What we claim as our invention is:

l. A method of detecting breaks in a flexible elongate member whose surface is of an insulating material capable of generating an electrostatic charge by friction with another surface comprising causing the member to travel in the direction of its length past and in continuous contact with at least one electrode which is connected to a charge sink, said electrode being conductive and of a material chosen to cause electrons to be transferred continuously in one direction between said electrode and the surface of said member and to flow between the said charge sink and said electrode, and continuously monitoring the current flowing between said electrode and said charge sink to observe whether it falls below a predetermined value.

2. A method in accordance with claim 1 comprising applying a dc voltage with respect to the said charge sink to said electrode.

3. A method of detecting breaks in an insulated electric conductor whose surface is ofa material capable of generating an electrostatic charge by friction with another surface, comprising causing the insulated conductor to travel in the direction of its length past and in continuous contact with at least one electrode which is connected to a charge sink, said electrode being conductive and of a material chosen to cause electrons to be transferred continuously in one direction between said electrode and the surface of said insulated conductor and to flow between the said charge sink and said electrode, and continuously monitoring the current flowing between the said electrode and said charge sink to observe whether it falls below a predetermined value.

4. A method of detecting breaks in an insulated electric conductor whose surface is of a material capable of generating an electrostatic charge by friction with an other surface comprising causing the insulated conductor to travel in the direction of its length past and in continuous contact with at least one electrode maintained at a fixed dc voltage with respect of a charge sink, said electrode being conductive and of a material chosen to cause electrons to be transferred continuously in one direction between said electrode and the surface of said insulated conductor and to flow between the said charge sink and said electrode, and continuously monitoring the current flowing between said electrode and said charge sink to observe whether it falls below a predetermined value.

5. A method as claimed in claim 4 in which said voltage is at least 50 volts.

6. A method as claimed in claim 4 in which said voltage is about 200 volts.

7. A method as claimed in claim 3 comprising connecting said electrode to earth through a high-value detector resistor and observing the voltage across said detector resistor.

FORM PO-1050 (10-69) UNITED STATES PATENT OFFICE CETIFTCATE OF CORRECTION Patent No. 3 859 593 Dated January 7 1975 n (s) John Huvton Poole and Brian Anthony Goodison It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The Assignee should read:

BRITISH INSULATED CALLENDER'S CABLES LIMITED Signed and Sealed this ninth Day Of September 1975 [SEAL] Arrest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN (mmnisxinncr nfPau'nrs and Trademarkx USCOMM-DC 60376-P69 9 us. GOVERNMENT PRINTING OFFICE: I969 0-366-334, 

1. A method of detecting breaks in a flexible elongate member whose surface is of an insulating material capable of generating an electrostatic charge by friction with another surface comprising causing the member to travel in the direction of its length past and in continuous contact with at least one electrode which is connected to a charge sink, said electrode being conductive and of a material chosen to cause electrons to be transferred continuously in one direction between said electrode and the surface of said member and to flow between the said charge sink and said electrode, and continuously monitoring the current flowing between said electrode and said charge sink to observe whether it falls below a predetermined value.
 2. A method in accordance with claim 1 comprising applying a dc voltage with respect to the said charge sink to said electrode.
 3. A method of detecting breaks in an insulated electric conductor whose surface is of a material capable of generating an electrostatic charge by friction with another surface, comprising causing the insulated conductor to travel in the direction of its length past and in continuous contact with at least one electrode which is connected to a charge sink, said electrode being conductive and of a material chosen to cause electrons to be transferred continuously in one direction between said electrode and the surface of said insulated conductor and to flow between the said charge sink and said electrode, and continuously monitoring the current flowing between the said electrode and said charge sink to observe whether it falls below a predetermined value.
 4. A method of detecting breaks in an insulated electric conductor whose surface is of a material capable of generating an electrostatic charge by friction with another surface comprising causing the insulated conductor to travel in the direction of its length past and in continuous contact with at least one electrode maintained at a fixed dc voltage with respect of a charge sink, said electrode being conductive and of a material chosen to cause electrons to be transferred continuously in one direction between said electrode and the surface of said insulated conductor and to flow between the said charge sink and said electrode, and continuously monitoring the current flowing between said electrode and said charge sink to observe whether it falls below a predetermined value.
 5. A method as claimed in claim 4 in which said voltage is at least 50 volts.
 6. A method as claimed in claim 4 in which said voltage is about 200 volts.
 7. A method as claimed in claim 3 comprising connecting said electrode to earth through a high-value detector resistor and observing the voltage across said detector resistor. 